Recursion
by Leyrann
Summary: Harry Potter is the only survivor of the Battle of Hogwarts. Among the ruins of the castle, he resolves to find a way to travel to the past and use his knowledge of the future to his advantage. And if that isn't enough... well, he has very special trick up his sleeve. **ON HIATUS**


**AN: I'm going to give writing two stories at the same time a try, as I think it may increase my total writing speed. For the coming weeks, I will alternate between a chapter of this and a chapter of The Advantages of Being Sane, if it doesn't work out I will put this story on hiatus until Advantages is done.**

**AN: This is one half of the split of (old) Recursion, the first I ever uploaded. I will write the other story (Draco Malfoy traveling back in time, which was the 'hook' for the old Recursion) at a later date, likely after finishing Advantages.**

**Disclaimer:** I do not own Harry Potter.

* * *

**Prologue: Another chance**

* * *

Harry Potter overlooked the ruins of Hogwarts. After Dumbledore's death, everything had gone to shit, and that was putting it gently. Voldemort overtook the Ministry and started exterminating muggleborns. Halfbloods were regarded with suspicion, and purebloods were investigated to ensure they had no ties with the first two groups – let alone muggles. Throughout the year, he and his friends had been on a fruitless hunt for horcruxes. They hadn't found a single one. They hadn't even been able to recover the real Locket. And then, when they'd come to Hogwarts in the hopes of sneaking into the Headmaster's office and talking to Dumbledore's portrait, plus a vain hope they would somehow stumble across a horcrux in the only place Voldemort had ever called home, they'd been found out, and before the day was out the Battle of Hogwarts had begun.

Voldemort had obliterated all opposition, and one by one Harry's friends had died. The only reason he himself was alive was because Severus Snape – _of all people_ – had lured him away from the battle when it became clear they were losing. The man had given him a set of memories to watch as soon as he got the chance, claiming there was no time to explain. Then, he had given his life to allow Harry to escape, knowing prophecy had designated him as the only one who could defeat Voldemort.

Harry had just watched the series of memories. It didn't give him much hope. Yes, it taught him about Snape, but there was no secret key to winning the war. In fact, the only part important to the war it had taught him was that he, himself, was a horcrux. Which, truth be told, did answer some questions.

But it was all for naught. That knowledge was useless. By Harry's count, four of Voldemort's horcruxes were still intact – five, if you counted Harry himself. The Locket, wherever it was, the snake, the one that was most likely Hufflepuffs Cup, and a last horcrux of which he did not even have an idea what it could possibly be. He had no allies, no friends, nothing. After the Battle of Hogwarts, Voldemort's rule of Magical Britain was absolute.

At that moment, Harry James Potter, the Boy-Who-Lived, the Chosen One, wanted to just give in. To end it all. It was over. Lost.

All strength left his legs and he sagged to the ground. Next to him stood the Pensieve, which he'd recovered to watch the memories, hoping for a thread. A reason to live. A way to defeat Voldemort. With an angry shout, he grabbed the artefact and flung it across the ruins, and it crashed into a thousand pieces.

If only Dumbledore had still been alive, but even his portrait had perished in the destruction of the castle. Dumbledore had always known the answer. He had always found a way. Even his own death had been planned almost a year in advance. He had send Fawkes when Harry found himself pitted against a phoenix. He'd prepared for Voldemort when the rest of the country refused to acknowledge his return. He'd shown up from wherever he was hiding when Harry had foolishly ran to the Ministry, believing Sirius had been captured, to duel Voldemort himself.

Sirius… Harry still remembered at the end of his third year, when Sirius had been captured just after they'd learned the truth, how all hope had been lost. The Minister was there, a dementor was coming, and Sirius had been locked up. And once again, Dumbledore had found a solution. They had traveled back in time to save him, and Buckbeak in the process.

Traveled… back… in time.

An ember of hope alighted in his heart. He'd never – _never_ – heard of any kind of time travel that allowed him to travel sufficiently far back in time to do something about this mess; in fact, he hadn't ever heard of any kind of time travel other than with time turners. But this… this was at least something he could search for. A purpose. A reason to carry on. To continue fighting.

Resolutely, he came to his feet and started making his way to where the library had been. Perhaps he could find something among the books that had been in the Restricted Section.

* * *

Twice a day, Harry Apparated to a nearby town or village to steal some food. With the wards of Hogwarts being gone, he then immediately Apparated back with the food to eat it while continuing his search for something – _anything_ – useful. He'd been at it for several months by now, sleeping in a small room that had somehow remained intact even though almost the entire castle was in ruins, and spending his entire day, every day, looking through all books he could find. Many books had been damaged in one way or another, but luckily there hadn't been a fire. If there had been, Harry would have probably had to give up.

Instead, he moved from one book to another, often barely reading more than just the table of contents. _Necromancy Unveiled_. No. A banishing charm threw it into the ever growing pile of books he'd gone through. _Charms of the Orient_. Harry perused the subjects. Nothing even remotely in the right direction. Banish. _Lifeline: A Study of Blood Magic_. Useless. Sometimes, Harry found it hard to carry on, all alone. But he had no other choice.

The next book seemed to be written in Latin. A few months ago, he might have thrown it away without a second look, but he'd become more desperate since then. Luckily, he'd come across a book that contained a spell that allowed him to translate Latin into English even if he didn't understand the Latin. It was a process that heavily drained his core, but he still regularly used it to translate titles and tables of contents.

As he cast the spell, the letters on the cover glowed bright for a few seconds as they changed and rearranged into English. _The Secrets of Wand Bonds_, the book now read. He sighed, but still opened the book. Even if it wasn't going to bring him any closer to his goal, knowing more about wands – like the very fact that such a thing as a Wand Bond exists – could prove useful.

_Part I: The working of wands  
__Chapter 1: The introduction of wands in the Roman Empire  
__Chapter 2: Wand movements  
__Chapter 3: Incantations  
__Chapter 4: Silent and point casting_

_Part II: Wands and other foci  
__Chapter 5: An explanation of the potency of a wand as focus  
__Chapter 6: Staves  
__Chapter 7: Other foci_

_Part III: The bond between wand and soul and the Great Ritual  
__Chapter 8: Workings of the Wand Bond  
__Chapter 9: The wand in soul magic  
__Chapter 10: The formation of the bond and the importance of the bond day  
__Chapter 11: Why the Great Ritual can send the soul back  
__Chapter 12: Requirements for the Great Ritual_

Harry stared at chapter 11. Could this be… Quickly, he paged to the chapter and cast the translation spell, leaving him winded. He perused the contents, which went in great depth on the topics of arithmancy and ancient runes. During his search, Harry had really come to regret not taking those subjects. The description of various pieces, however, certainly made him think he'd finally found what he had been looking for, with phrases like "_the day the Wand Bond is formed fixes the soul in time_" or "_time is, in the end, nothing more than a direction. Though the soul normally moves forward, it may just as well move backward. Contrary to normal directions, however, traveling in the other direction changes the intermediate area by its very nature._"

Still, Harry realized he needed to know the effects of the ritual, not it's inner workings. He was already tired after translating one chapter, but after a few seconds of hesitation, he went to chapter 10 and translated it.

He promptly slipped backwards in a coma-like sleep, completely spent.

* * *

When Harry had first woken up, it had been dark, so he had dragged himself to his makeshift bed and gone back to sleep. Dawn had woken him up again, and immediately after he'd filled his rumbling stomach he grabbed the book and started reading. Excitement fluttered through him when he realized that, yes, this so-called "Great Ritual" indeed allowed his memories to travel back in time, to a single predetermined moment. The moment he first touched his wand. Contrary to bodily traveling back in time, his memories would be imprinted on his younger self. From what he understood of the chapter he'd read yesterday, this would, in a way, immediately shift the future around, as the memories would change his actions.

Still, Harry did his best to remain calm and not celebrate too early, as he had yet to read chapter 12, which detailed how to actually perform the ritual. So after he finished reading the entirety of chapter 10, he again cast the translation spell and started meticulously going through chapter 12.

* * *

Preparing and performing the ritual had taken several weeks, and Harry would never have managed it if the dungeons – and their potions stores – hadn't still been intact. But finally, he had reached the end of the instructions. With but a moment of hesitation – this was the only chance he had – he dipped a goblet into the potion he'd brewed and then drank it in a single go. He held up his wand in front of him, standing among the runes he had drawn on the ground, and started the chant he'd learned by heart over the weeks. As the incantations continued, his wand started glowing softly, then more and more powerful. He uttered the last word, and the wand exploded in blinding light, leaving him unable to see anything else.

After a few seconds, the light receded, and he found himself in a dark shop, his eyes some twenty, thirty centimeter closer to the ground than he was used to. It had worked! Right in front of him, Ollivander stared at him, open-mouthed.

Oh.

Crap.

"I had heard about this… reaction," the man said slowly. "But I had never expected to witness it myself. Do I need to be worried?"

"Only about Lord Voldemort," Harry said, looking around to make sure no one else was around.

"Then I wish you luck, Mr Potter. I shall keep your secret. Such is the responsibility of a wandmaker."

"Thank you, Mr Ollivander. Secrecy will be essential."

* * *

After the opening feast, Harry made his way through the crowds to Dumbledore.

"Headmaster!"

The man looked at him with those twinkling blue eyes and a kind smile. "Ah, Harry Potter. How do you like your housemates?"

Harry smiled. "They're quite nice, Headmaster. I want to tell you something though," he looked around quickly, "but I'd prefer to do that in your office. Would you mind taking me along for a moment?"

"My, Harry, what could possibly be so important?"

"In your office?"

"Of course, of course, come along."

Dumbledore led the way to his office and sat down behind his desk, gesturing for Harry to take the seat in front of said desk.

He spread his hands. "So, what is it you wish to know?"

"Headmaster, I'm afraid I have… somewhat bad and somewhat good news, I suppose." He took a breath. Best to get it over with in one go. "After losing the war against Voldemort, I have traveled back in time to stop his victory, and I was hoping you could assist me in doing so."

Dumbledore held up his hand before Harry could continue. "You say you have traveled back in time? I hope you understand I need to ask you for proof," he said.

"The one with the power to vanquish the Dark Lord approaches," Harry quoted. "born to those who have thrice defied him, born as the seventh month dies… and the Dark Lord will mark him as his equal, but he will have power the Dark Lord knows not… and either must die at the hand of the other for neither can live while the other survives… the one with the power to vanquish the Dark Lord will be born as the seventh month dies…"

"I see…" Dumbledore said. "It is a good thing you came to me with this, Harry. Even for a cause like this, it is far too dangerous to mess with time." Before Harry had time to react, Dumbledore had taken out his wand and pointed it towards Harry.

"_Obliviate_."

And Harry Potter knew no more.

* * *

_Four years later…_

* * *

"_Legilimens_!"

Snape's office vanished and images raced through Harry's mind.

He was five, watching Dudley riding a new red bicycle, and his heart was bursting with jealousy. … He was nine, and Ripper the bulldog was chasing him up a tree and the Dursleys were laughing below on the lawn. … He was sitting under the Sorting Hat, and it was telling him he would do well in Slytherin. …

Suddenly, the flood of images stopped.

"Potter, are you aware there is a memory lock in your mind?"

"A what?"

"A memory lock. You have been obliviated. I am also almost entirely certain no false memories have been added to your mind. Is there perhaps a gap in your memories?"

Obliviated? When? Suddenly, his mind went to Lockhart, who he had seen just a few weeks back at St Mungo's. His thoughts went over the various events in second year… but if he had been obliviated by Lockhart, then why did he remember Lockhart as a coward? Surely Lockhart would have changed that…

"I don't know," he said. "I can't think of any suspicious gaps. Would it be something like a single conversation, or something longer?"

"I cannot say at this time. Considering how quickly I came across it, it may be quite a big lock, perhaps even weeks or months, but it could be a coincidence."

"I think I would have realized that," Harry said. "Can the memory be restored?"

"If you improve your occlumency, the lock may come loose," Snape said. "I may also be able to better judge the size of the memory lock if we continue your lessons."

Harry nodded. "Then let's continue."

* * *

Occlumency proved a very difficult discipline to learn, but knowing some of Harry's memories had been hidden away by someone turned out to be a great motivation. Over several weeks, Snape had come to the conclusion the memory lock contained at least several months of memories, leaving Harry completely stumped as to what they might contain. Despite that, the occlumency had aided Harry into recognizing the existence of the lock within his own mind. Once again, he entered Snape's office for a lesson. Though he still had little respect for the man, he had to admit Snape did look to aid him in recovering the memories.

"No legilimency attacks today," Snape said. "Instead, we will see if we can break the memory lock. Perhaps that will answer the questions we have. As we established, you are aware of the lock in your mind. You will keep your focus on the lock and I will probe you with simple wandless legilimency to shake the lock loose."

The prodding continued for two hours, with Harry doing his very best to keep his attention on the lock and his eyes meeting Snape's. Suddenly, the lock broke, causing Harry to faint immediately.

* * *

Harry woke up to a spicy taste in his mouth. He leaned back in his chair, trying to make sense of the mess in his mind. It took him several seconds, but whatever potion Snape had fed him certainly helped. When everything had ordered itself, his reaction was immediate.

"I'm going to kill that bastard!" He leapt out of the chair he was sitting on and made for the door, fumbling for his wand at the same time.

"POTTER!" Snape thundered, stopping him in his tracks. He turned around, almost flinching at the expression of anger on Snape's face. "Sit down. Now."

Harry considered the option of disobeying for a moment, but decided it was not worth it, so he moved back and sat down.

"When did the events that were locked away take place?" Snape asked.

"I was obliviated near the start of my first year," Harry said, trying to figure out how to explain his time travel and desperately hoping Snape wouldn't side with Dumbledore.

"Then I assume it was the Dark Lord who took away memories of yours while possessing Quirinius?"

"No, sir. It's… more complicated than that."

"How long do the memories span?"

"Seven years," Harry said.

"Potter, are you implying you forgot half your life – more, at the time it happened, and you did not realize something was wrong?"

"I used a ritual that allowed my memories to travel several years back in time," Harry said, "and everything that happened between my sorting and using the ritual was taken away from me. That's why I did not notice any gaps in my memory. There weren't any, when not accounting for the time travel."

"You are testing my patience, Potter."

Harry thought for a moment, then spoke again. "Your Patronus is a doe."

Snape froze. "How much do you know?"

"About you? Only the memories you gave me before you held up Voldemort so I could escape, which dealt primarily with your friendship with and memory of my mother."

"What made you perform this ritual?"

"Voldemort had won. He controlled the Ministry, muggleborns were prosecuted, the Order of the Phoenix was no more because everyone had been killed, and nothing but ruins remained of Hogwarts. To my knowledge, I was the only one left alive to oppose Voldemort, and though I knew how he had made himself immortal, I was in absolutely no position to counter that. I think, if I had not had the idea of searching for a way to travel back in time, I would have instead ended my own life. No one would have missed me, and I could not possibly have resisted Voldemort on my own."

"And who obliviated you of this knowledge?" Snape asked in a dangerous tone. "I cannot think of anyone but the Dark Lord who would stand to gain by doing so, but you said it wasn't him."

"Not he," Harry confirmed, anger rising again as he thought of what had happened. "_Dumbledore_. He would rather see the world in ruins than take his chances with time travel."

"He would do that?" Snape asked in disbelief.

"I would not have believed it either," Harry said. "When I arrived here at Hogwarts, I went to him immediately after the opening feast with the intention to tell him everything I knew. He told me it was dangerous to mess with time and obliviated me before I had a chance to react. In case you're wondering, everything since has happened exactly as it did first time around. Up to and including me getting a lucky strike in against a basilisk and surviving Voldemort's resurrection with an _Expelliarmus_. Until the moment you noticed my memory lock, nothing was different."

Snape shook his head. "I can hardly believe Albus would do something like that, and yet, I can already see him rationalize it. Most likely, he even obliviated himself of the knowledge you performed time travel. Which in itself… how did you _do_ that?"

"It's a part of wand design," Harry answered. "When a wand chooses a wizard, it forms a bond with that wizard. One of the most secret side effects of that bond is that it allows you to send your memories back to the moment the bond formed if you perform a complicated ritual. I found a Latin tome in the remains of the Hogwarts library that described the ritual, and after I went back in time Ollivander confirmed he was aware of the existence of the ritual, but promised to keep my time travel to himself."

"Every wizard could perform it?" Snape asked, incredulous.

"Every wizard with six years of magical education, a knack for practical magic and a strong enough drive. But yes, the workings of the ritual or even where it can be found aren't something that should be announced everywhere. In fact, if you do not mind, professor, I'd prefer to not even tell you."

Snape nodded. "I understand. Now, I suppose the question remains: you are now the most knowledgeable person about this war, assuming Albus had passed all his knowledge on to you, and you know what is going to happen the coming… two years? So what are you going to do?"

"In all honesty, sir, I don't know. I didn't have much faith even when I performed the ritual, and with the last four years taken away… I will do what I can, but I do not have much hope we can win this war."

Snape grimaced. "Is it that bad?"

This was a gamble. "Have you heard about horcruxes, sir?"

"I can't say that I have."

"A horcrux is an object in which a wizard can store a piece of their soul through a ritual, which includes a cold-blooded murder, granting immortality until the container is destroyed. Voldemort has performed this ritual not just once, but six separate times. One was responsible for the opening of the Chamber of Secrets and has been destroyed, one is currently in the headquarters of the Order, stolen by Regulus Black, one will be found by Dumbledore this summer, but at the cost of his arm and eventually his life unless we interfere, one is Voldemort's own familiar, of the fifth I only know what item it most likely is, while I don't have the foggiest where it could be, and of the last one I know absolutely nothing at all, except that it's likely to have some kind of connection to the Founders of Hogwarts. Unless they can all be found and destroyed, Voldemort is immortal. After Dumbledore's death I have spent a year looking for them with Ron and Hermione, without even finding a trace of one."

Snape looked grey. "How can you find them?"

"Honestly? It would probably have to come down to sheer luck. There is simply too much we do not know about Voldemort to correctly determine the last horcrux, let alone where he might have hidden his horcruxes."

"What do you think your chances are?"

"Low. Perhaps, if I'd have had seven years, I could have done it, but I only have two and a half."

"So you need more… time…" Snape trailed off.

A thoughtful look appeared on Snape's face, until he spoke again after several seconds.

"Would it be possible to perform the ritual a second time?"

Harry just stared at him, slack-jawed.

"That's brilliant!" he exclaimed after his brain restarted. "I could simply repeat the ritual if things don't work out, however long is needed until everything _does_ work out and we defeat him. I would need your help in getting the book, however, as I expect it would be in the Restricted Section, and I would also prefer if you could brew the potion that is part of the ritual, as it would be hard for me to do so in between classes. Could you do that for me, sir?"

"You believe it is a good idea to immediately perform this ritual? Wouldn't it make more sense to see what you can learn before doing it?"

"Sir, with the last four years not having changed, I haven't managed to delay Voldemort's return, haven't made the Ministry more open to the idea of his return, have wasted several chances to obtain horcruxes, and I already know looking for horcruxes without a plan is useless. With the ritual requiring several weeks of preparation, I might as well do it now. That would leave me with much more time to gather information and devise plans, while being at far less risk. If Voldemort were to get me, and he came quite close at the end of my fifth year - though mostly because of my own fault - it would be too late. It would be far safer to work in a world where he has not yet returned."

"Then I shall write your pass for the Restricted Section. Simply give me the recipe of the potion and I will brew it for you. I believe you mentioned there were other requirements too?" Harry nodded. "Then I will select an empty classroom in the dungeons where you can perform those preparations."

"Thank you, sir. If I may make a proposal, we can meet about this under the guise of occlumency lessons to those in the know and remidial potion lessons to those not in the know?"

Snape nodded. "Now go, this evening has become late enough already."

Harry did so, and felt hope like he hadn't felt in a very long time. If he failed, he could simply try again. And again. However many times he had to try to defeat Voldemort. The only condition was that he had to survive to perform the ritual.

* * *

Several weeks later, Harry once again found himself in the center of a mass of runes. Professor Snape had given him the potion yesterday, and once again he drank it in a single gulp, then started his chant, wand raised high in front of him. Slowly, it began to glow, brighter and brighter, until he finished the chant, and it exploded in light.

* * *

**AN: First things first, despite what I said at the start, I may not start updating this story quite yet the coming weeks, as I'm first going to work on an outline, which will take up the time set apart for Recursion. So if this remains silent for a few weeks, then it's because I'm outlining.**

**AN: This story is also something of a criticism towards time travel stories that use a method that can be repeated. Because if that is the case, then can you not just repeat it however many times is needed to obtain the desired result? I should mention that, despite multiple instances of time travel occurring during this story, this is **_**not**_** a "I will keep writing until I get bored of it and send Harry back in time every now and then" story. It will have a gradually advancing plot and an ending.**

**AN: I also wish to mention this isn't an _evil_ Dumbledore. I just decided to hit two birds with one stone by closing off the avenue of "confide in Dumbledore and let him sort everything out" and at the same time creating a plot that allowed me to put the twist in the prologue.**


End file.
